If 'Blue Light' is Bad For Us, Which Type of Light is Good?

Science Says: 'Blue Light' is Bad for Us, Green Light May Be Good

The good and bad effects of light exposure have “come to light” in recent studies that have
investigated the positive effects of sunlight on health and the negative effects of exposure to artificial light, particularly at night.

While full-spectrum lighting mimics the effects of sunlight with its full complement of colors, most modern artificial lighting varies in its wavelengths.

Indeed, the significant blue component of light from sources such as computer monitors and other electronic device screens (particularly light-emitting diodes, or LEDS) has been blamed for an array of symptoms including eye strain, headaches, and insomnia.

But while blue light appears to be harmful in some respects, green light is a horse of a different color.

It’s been said that living in an area with a high amount of green space can reduce the impact of stressful life events.1 Other research has found an association between the quantity and quality of green areas and streetscape greenery on indicators of health.2 Another study revealed what appears to be a protective effect of access to urban green space against anxiety and mood disorders.3 According to an article in the February 1, 2018 issue of Bioscience, several biologically plausible theories have been proposed to explain this effect. These include attention-restoration theory, stress-reduction theory, and biophilia theory.4 Could something as simple as color also play a role?

Could Green Light Relive Pain?

In recent research, Mohab M. Ibrahim and colleagues at the University of Arizona found that exposure to green LED light increases pain tolerance in rats, and that when the rodents were fitted with green contact lenses, a pain-relieving effect was also observed.5

The journey to Dr. Ibrahim’s discovery of the benefit of green light began with his brother. His brother suffered from headaches and reported feeling better just by going outside to sit among the trees. "Sometimes I get headaches myself, so I go to a park and sit there, and I do feel better,” Dr. Ibrahim stated. “I thought, why is this happening? It could be because it's quiet. You're meditating, and life slows down, but I can also be quiet in my office, and it doesn't take the headaches away. Then I thought maybe it's the trees. So, I thought about what trees do. They could be releasing some sort of chemical in the air, or maybe it's just their color, green, which is associated with most trees."6

"While the pain-relieving qualities of green LED are clear, exactly how it works remains a puzzle," commented Rajesh Khanna, University of Arizona, Associate Professor of Pharmacology who is a senior author of the research report coauthored by Dr. Ibrahim. "Early studies show that green light is increasing the levels of circulating endogenous opioids, which may explain the pain-relieving effects. Whether this will be observed in humans is not yet known and needs further work."

The Best Lighting for Migraine Sufferers

The pain-relieving effect of green light could help migraine sufferers. Individuals experiencing migraines are particularly sensitive to light, prompting many of them to seek recovery in darkened rooms, which involves significant time spent absent from work or other duties. Research conducted by Rami Burstein, PhD, of Harvard Medical School, and colleagues, revealed that while blue light increases the pain of migraine, exposure to green light could reduce pain in approximately 20% of the patients. The group of scientists discovered that, of all colors, green light generated the smallest electric signals in the retina of the eye and in the brain’s cortex. Further investigation revealed that neurons in the thalamus of the brain, which transmits information concerning light from the eye to the cortex, are most responsive to blue light and least responsive to green.7

These findings helped the investigators conclude that the most photophobic blue light activates more neurons and causes a stronger response than the least photophobic green light. White light, which is more photophobic than green light, activates neurons more powerfully than green light, but less intensely than bluelight. “Therapeutically, filtering out all but green light may prove beneficial for the reduction of photophobia and potentially the headache intensity”, write the study investigators.

Effects of Light on Sleep

For those wishing to avoid some of the harmful effects of excessive blue light exposure, a variety of blue-blocking sunglasses are available as well as protective lenses that can be worn during the day. Computer screen protectors and applications that reduce exposure to blue light in the evening can help protect the eyes and improve sleep. It is recommended to take a break from bright light exposure at least one hour before going to bed in order to improve the release of melatonin, a hormone that facilitates sleep.

Related Article: How Much Melatonin Should I Take?  

A study that examined the effects of blue or green light on sleep found that blue light kept mice awake longer while green light was conducive to sleep. Researchers Violet Pilorz and colleagues determined that a light sensor in the eye known as melanopsin is critical to the response.8 And while both blue and green light increased corticosterone levels compared to animals exposed to no light, levels were higher among mice exposed to blue light than among those exposed to green light.

“These results reinforce the idea that blue light exerts a powerful alerting effect compared to green light,” write Patrice Bourgin and Jeffrey Hubbard in an article in the same journal. The authors point out that the possibility to use different wavelength compositions to stimulate alertness or help sleep may lead to additional indications of light therapy as a complementary approach to help patients with insomnia or excessive daytime sleepiness.9

In discussing the article by Pilorz and colleagues, the authors explain that the findings open the need for a better understanding of melanopsin-based phototransduction. Based on their research results, color wavelength is another aspect of environmental illumination that should be considered in addition to photon density, duration of exposure, and time of day when designing lighting to improve human health and well-being.


  1. van den Berg AE, et al. Soc Sci Med. 2010 Apr;70(8):1203-10.
  2. van Dillen SM, et al. J Epidemiol Community Health. 2012 Jun;66(6):e8.
  3. Nutsford D, et al. Public Health. 2013 Nov;127(11):1005-11.
  4. Bakolis I, et al. Bioscience. 2018 Feb 1;68(2):134-145
  5. Ibrahim MM, et al. Pain. 2017 Feb;158(2):347-360
  6. https://uanews.arizona.edu/story/treatment-pain-gets-green-light
  7. Noseda R, et al. Brain. 2016 Jul;139(7):1971–1986.
  8. Pilorz V, et al. PLoS Biol. 2016 Jun 8;14(6):e1002482.
  9. Bourgin P, et al. PLoS Biol. 2016 Aug 15;14(8):e2000111.


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